Remove variables that aren't being used right now

Found by ICC.

 src/quick/items/qquicktextcontrol.cpp(78): error #2415: variable "fullWidthSelection" of static storage duration was declared but never referenced
 src/quick/items/qquicktextinput.cpp(2696): error #2415: variable "textCursorWidth" of static storage duration was declared but never referenced
 src/quick/items/qquicktextinput.cpp(2697): error #2415: variable "fullWidthSelection" of static storage duration was declared but never referenced
 src/quick/scenegraph/qsgthreadedrenderloop.cpp(164): error #2415: variable "WM_LockAndSync" of static storage duration was declared but never referenced
 src/quick/scenegraph/qsgthreadedrenderloop.cpp(181): error #2415: variable "WM_UpdateLater" of static storage duration was declared but never referenced

Change-Id: I60b5cce79d7be5f909b690f97ffa93ea00d3c044
Reviewed-by: Alan Alpert <aalpert@blackberry.com>